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Soft-decision decoding techniques are applied the size of code alphabet of binary convolutional codes and to asynchronous frequency-hop/spread-spectrum multiple-access binary turbo codes does not match the modulation order (FHISSMA) networks, where M-ary frequency shift keying M, the asynchronous FH/SSMA networks employing soft-(MFSK) is employed to transmit one modulated symbol per hop. '. .Coding schemes using soft-decision decoded binary convolutional dision deoedvina convolt codes or turbo codes codes or turbo codes are considered, both with or without bit-without bit-interleaving can support much more users than interleaving. Performances of several soft metrics are examined those employing hard-decision decoded RS codes. for each coding scheme. It is shown that when multiple access interference is the main source of errors, the product metric II. SYSTEM MODEL offers the best performance among the soft metrics considered The asynchronous FH/SSMA networks considered here are for all coding schemes. Furthermore, the application of softdecision decoded convolutional codes or turbo codes without similar to those in [2]. In these network, U transmitters and U bit-interleaving is shown to allow for a much larger number receivers are connected in a pairwise topology. Each transmitof simultaneously transmitting users than hard-decision decoded ter communicates with its receiver using error correction codes Reed-Solomon codes. and frequency-hopping with MFSK modulation. We focus on soft-decision decoded convolutional codes and turbo codes for I. INTRODUCTION error correction. The turbo code considered in this paper isIn this paper, we consider asynchronous frequency-the parallel concatenation of two identical recursive systematic hop/spread-spectrum multiple access (FH/SSMA) networks in convolutional (RSC) codes (henceforth denoted as component which each user employs noncoherent M-ary frequency shift codes) connected via an interleaver. keying (MFSK) modulation to transmit one M-ary symbol per A Packet Encoding and Transmission hop. In these asynchronous networks, the interfering signals are not orthogonal at the receiver due to random delays of At the transmitters, each data sequence is encoded by different users. Thus, an interfering signal arriving at a non-error correction codes (convolutional codes or turbo codes) coherent receiver with a nonzero delay will affect the outputs and then interleaved (bit-interleaved or symbol-interleaved) to of all the M correlators in the receiver which is called the form a packet. Here, bit-interleaving means that binary coded multiple-access interference (MAI). Forward error correction sequences are first randomly interleaved and then mapped codes provide an effective mean to combat the effects of into sequences of M-ary symbols, while symbol-interleaving MAI. Most of the previous work on coded asynchronous means that binary coded sequences are first mapped into FH/SSMA networks has focused on error correction codes sequences of M-ary symbols and then randomly interleaved. wi...